1. Field Of The Invention
The invention generally relates to electrical connectors, and more specifically to insulation displacement connectors for printed circuit boards and the like.
2. Description Of The Prior Art
Insulation displacement connectors ("IDCs") have become popular since they are highly economical and a cost-effective method for performing wire terminations. No wire or cable preparation is required. IDCs are designed to reduce wire termination cost by eliminating the need to remove the insulation from the wire before terminating it. The connection to the wire is made by pushing it into a narrow slot or wire receiving channel between two fairly rigid contact beams or tines of the contact. The conductor slot is smaller than the conductor diameter. When a wire is inserted into the IDC slot, the lead-in chamfers cut and displaces the wire insulation. As the wire is pushed further down into the slot, there is a deformation of both the conductor and the IDC beam. The conductor will have mostly plastic deformation while the contact beams will have elastic deformation (deflect outwardly). Such deformation is proportional to the normal (contact force) which acts on the conductor and on the beam interface. This normal force is very important to establish and maintain a good gastight connection.
Several degrading mechanisms work against such gastight connection. The most significant factors include:
(a) creep which is the change in deflection or deformation over time with constant force. In the case of IDC termination, the wire creep is a significant factor. Also referred to as "sizing" which is defined as reduction of the wire diameter due to environmental conditions;
(b) Stress relaxation, which is the reduction in force over time with constant deflection. This factor largely depends on the initial stress level and the temperatures. Stress relaxation in the contact beams will reduce the normal force acting on the wire and/or its insulation;
(c) Movement between conductor and contact which is caused mainly by wire flexing, pulling, and the difference in thermal expansion coefficients of the conductor and the contact material. Those movements are especially degrading in the case of stranded wire because it helps the wire strands to rearrange in a narrower shape with lower energy level. Such movements can take place over time as external forces act upon the various strands and cause them to realign between the connector contacts.
All of the aforementioned degrading mechanisms cause normal (contact) force reduction, which depends on the contact spring rate. The short stiff beams of the conventional IDCs exhibit a high degree of rigidity and provide very little deflection. After wire sizing the contact force is largely reduced. Also, the stiff contact beams do a poor job in rearranging the wire strands into the narrowest width shape.
Numerous IDC designs have been proposed. U.S. Pat. Nos. 3,950,065; 3,937,549 and 4,074,929 disclose typical known IDC designs. It will be noted that many of these IDCs also provide strain relief by capturing the wire insulation and preventing longitudinal and other forces from acting on the conductors in the plane of the IDC contacts. Whether or not strain relief is provided, however, prior IDCs are formed as aforementioned, by a pair of spaced tines which are spaced to provide a wire receiving slot and are rigidly joined to each other at the closed end of the slot, thereby preventing movements of the tines relative to each other in the contact plane. Such design has imparted the undesirable stiffness or rigidity which has been discussed above.